1. Field of the Invention
The present invention is directed to chemical microsensors. More particularly, the present invention is directed to fixed parallel plate chemical microsensors and microsensor arrays and methods of making same.
2. Background Information
Sensors based on micro electromechanical systems (MEMS) devices are useful for sensing a wide range of chemical conditions, such as the presence of volatile organic compounds (VOCs), hydrocarbon gases, and other analytes. Manufacturing techniques for building MEMS sensors, especially integrated circuit arrays of such sensors, usually involve many fabrication steps. Unfortunately most, if not all, of the sensor functionality has to be built into the microchip up front, making it difficult to customize or tune a sensor to fit a particular need after manufacture. For example, the dielectric material of a parallel plate capacitor sensor is usually deposited onto a first conductive electrode during an intermediate phase of the fabrication process, followed by deposition of a top plate electrode. Furthermore, MEMS devices are typically manufactured with solid dielectric materials whose physical properties require that layers be deposited in a specified order.
Other MEMS device configurations can be used as well to sense chemicals, for example, by measuring the capacitance changes of chemically sensitive materials with an inter-digitated finger capacitor or changes in physical properties with a cantilever. However, these arrangements often call for semi-rigid or flexible conductors that suffer from several disadvantages, including excess stray capacitance, stiction, and sensitivity to vibrations.